A radio frequency unit (RU) receives a baseband signal received by the radio frequency unit and up-converts the received baseband signal into a radio frequency signal, amplifies the up-converted radio frequency signal by a power amplifier, and then transmits the amplified signal through an antenna. In addition, a bandpass filter and a feedback unit may be connected to an output terminal of the radio frequency unit to remove a signal included in a frequency out of an operation frequency and to monitor an output signal.
The radio frequency unit monitors the output signal through the feedback unit, thereby performing operations of synchronizing the input/output signals, identifying and compensating for nonlinearity of the signal amplified by the power amplifier, and reducing magnitude of a peak of the signal. The radio frequency unit may transmit an undistorted output signal to other entities by the operation of the synchronization, the operation of compensating for the nonlinearity of the amplified signal, and the operation of reducing the magnitude of the peak of the signal.
However, the radio frequency unit receives and processes a baseband signal. The radio frequency unit may not know in advance whether the baseband signal is input at specific timing and magnitude and characteristics of the baseband signal when the baseband signal is input. Therefore, there arises a problem in that the operation of the synchronization and the operation of compensating for the nonlinearity of the amplified signal are not performed smoothly.